It is believed that the first implantable defibrillator was implanted in a patient in 1980. Currently, thousands of individuals have devices implanted to correct cardiac conditions involving lethal tachyarrhythmias. It is anticipated that approximately 20,000 patients a year will receive these devices by the mid 1990's. As the use of the implantable defibrillator becomes more prevalent, insuring the safety of the device becomes more crucial.
A structure common to all implantable defibrillators is the high voltage output stage. Typically it is the interface between the high voltage energy storage capacitor (which is charged by a DC to DC converter) and the patient. An example of this is disclosed in U.S. Pat. No. 4,800,883.
A serious hazard to the patient exists if the electronic switches used in the output stage fail such that one or more becomes a comparatively low resistance. If this should occur, the output of the DC to DC converter is connected directly to the patient during high voltage capacitor charging. The resultant current flowing through the heart of the patient can initiate or accelerate an arrhythmia, cause direct tissue damage, or possibly result in death. While U.S. Pat. No. 4,164,946 refers to a fault detecting mechanism, this particular problem is not addressed. Furthermore, no currently available defibrillator incorporates an effective mechanism to guard against this hazard.
It is an object of this invention to provide a mechanism for preventing the high voltage charging circuit from being connected directly to the patient.
It is an additional object of this invention to provide the physician with a means to verify the integrity of the defibrillation output stage without delivering a shock to the patient.
Other objects and advantages of the invention will become apparent as the description proceeds.